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 ###Instrução: Qual colliery tem um número de mortos de 7?
 ###Tabelas: CREATE TABLE available_games (available_games_id AUTO_INCREMENT PRIMARY KEY, Title VARCHAR, Publisher VARCHAR, Developer VARCHAR, Release date VARCHAR, ESRB VARCHAR) CREATE TABLE group_i (group_i_id AUTO_INCREMENT PRIMARY KEY, Position INT, Played INT, Points INT, Wins INT, Draws INT, Losses INT, Goals for INT, Goals against INT, Goal Difference INT) CREATE TABLE ladies_european_tour_career_summary (ladies_european_tour_career_summary_id AUTO_INCREMENT PRIMARY KEY, Year INT, Tournaments played INT, Cuts made INT, Wins INT, 2nd INT, 3rd INT, Top 10s INT, Best finish VARCHAR, Earnings ( € ) VARCHAR, Money list rank VARCHAR, Scoring average VARCHAR, Scoring rank VARCHAR, Rolex ranking INT) CREATE TABLE 250_million_or_more_records (250_million_or_more_records_id AUTO_INCREMENT PRIMARY KEY, Artist VARCHAR, Country of origin VARCHAR, Period active VARCHAR, Release-year of first charted record INT, Genre VARCHAR, Claimed sales VARCHAR) CREATE TABLE mining_disasters (mining_disasters_id AUTO_INCREMENT PRIMARY KEY, Colliery VARCHAR, Location VARCHAR, Date VARCHAR, Year INT, Death toll INT, cause VARCHAR)  
SELECT Colliery FROM mining_disasters WHERE Death toll = 7